The Phase Inversion Emulsification (PIE) process is a method whereby the phases of a liquid-liquid dispersion interchange such that the dispersed phase spontaneously inverts to become the continuous phase and vice versa under conditions determined by the system properties, volume ratio and energy input.
The phase inversion process typically involves the solubilization of a resin and other components in an organic solvent or mixture of organic solvents that include a phase inversion organic solvent, which is typically chosen for its solubility in both organic and aqueous phases.
By way of example, a solvent-based phase inversion emulsification process is often used to form a polyester resin emulsion in the production of polyester-based toners. In the phase inversion emulsification process, the polyester resin is first dissolved in appropriate organic solvents, such as methyl ethyl ketone and isopropanol, to produce a homogenous organic phase, followed by addition of a fixed amount of base solution, such as ammonium hydroxide, to neutralize acid end carboxyl groups on the polyester chain. The neutralized polymer is subsequently converted to a uniform dispersion of polyester particles, or latex, in water by phase inversion.